Devices featuring the above are commonly known as “one out of N double block-and-bleed manifold”, wherein “N” is a digit above 1, and the phrases “one out of N” and “double block-and-bleed” are often abbreviated as “1ooN” and “dbb”. 1003 dbb manifolds are in particular used in “High Integrity Pressure Protection Systems” (HIPPS) for a fluid line, in particular in oil or gas piping systems. In such HIPPS, the three lines of the 1oo3 dbb manifold—it can also be two lines of 1002, or more (four lines or more)—each contact independent pressure transmitters or switches to the pressure to be monitored downstream of an ON/OFF-Valve. Whenever any of the pressure transmitters signals the pressure to exceed a critical value, the HIPPS closes the one or more valve(s). The pressure is measured by the pressure transmitters, the pressure transmitter signal is voted 20oo3 by the logic solver, when 2 of the 3 transmitters give high signal, the logic solver will close one or more valves to prevent further pressure increase.
Having three independent pressure transmitters ensures redundant measurement, and operation without interruption in particular during periodical inspection, testing, calibration, maintenance, repair or replacement (hereinafter summarized as “test and maintenance”) of the pressure transmitters: For inspection of any of the pressure transmitters, the related pipe branch is separated from the fluid pipe by closing its entry block valve, remaining pressure released from the pressure transmitter by opening its bleed valve to the ambience, and the pressure transmitter isolated from the ambience by closing its exit block valve. After inspecting and/or maintaining the pressure transmitter, any remaining pressure is released from the pressure transmitter by opening the exit block valve, then the pressure transmitter closed from the ambience by closing the bleed valve, and last the pressure transmitter re-connected to the fluid line by opening the entry block valve.
ASTAVA B. V., Meppel/NL provides an interlocking system for a 1oo3 and 1oo2 dbb manifold, based on a crank handle that is mechanically caught in a complex track, that only allows, by positioning and turning the handle, first to select a pipe Branch, then to close the entry block valve, then to open the bleed valve, and last to close the exit block valve of the selected branch. Smith Flow Control Ltd., Lynbrook/AU and Netherlocks Safety Systems, Alphen aan den Rijn/NL each provide elaborate loose key systems, wherein any key, if delivered from a control room, and applied to a compatible valve, allows the operator only to open or close this same valve. Both the known track-caught handle, and the known key systems, allow for building pipe branching manifolds according to the above.
In technical background of the invention, U.S. Pat. No. 4,429,711 A discloses a multivalve interlock and control system for connecting a pair of pipelines to a differential pressure measuring instrument. The known system has three valves, each driven by a swiveling handle, each of the handles having a circular control device, that has up to three notches for mechanically interacting with the other control device, so as to allow the valves to be opened or closed in a mechanically defined sequence, only.
Disadvantages of prior art: cumbersome to operate, not easy to adapt for remote operation like subsea operation.